The present invention relates to vehicle disc brakes, and more specifically, the invention relates to a system and method for electrically monitoring disc brake lining wear.
Virtually all wheeled vehicles utilize braking systems to selectively inhibit wheel rotation and, therefore, reduce vehicle speed. Braking may be accomplished by the use of a disc braking system whereby a friction force is applied at one or more wheel assemblies to inhibit wheel rotation. Numerous disc brake systems are known in the art. Typically, the vehicle operator would generate a brake signal through a pedal thereby activating the disc brake system. The system generally includes a rotor or disc secured to the vehicle wheel, a caliper assembly mounted to the vehicle chassis, and a pair of friction pads (also called brake pads or brake linings) disposed on opposite sides of the rotor. Upon activation of the disc brake system, the friction pads are moved toward one another into frictional engagement with the rotor thereby actuating the braking force and slowing the vehicle.
Repeated braking actuation commonly leads to a wearing of the friction pads and an overall reduction in thickness. Disc brake systems are designed to accommodate certain levels of wear by compensating for reductions in pad thickness. Continued pad wear, however, may lead to mechanical problems such as reduced braking efficiency and damage to the rotor and/or caliper assemblies. To overcome this, strategies have been developed to monitor friction pad wear and to alert the vehicle operator of excessive pad wear and potential mechanical problems.
The U.S. Pat. No. 4,850,454 issued Jul. 25, 1989 to Korody is an example of a disc brake lining wear sensor. In the Korody patent, the wear sensor comprises a plastic encapsulated sensor having a support bracket that is attached to the support member of the disc brake. As the inner and outer linings wear, a peripheral portion of the inner brake pad is displaced axially by the caliper piston. The peripheral portion wears away the sensor surface and engages a metal conductor to complete a circuit. In this manner, the inner brake pad wears away the sensor and completes the warning circuit.
The U.S. Pat. No. 4,606,435 issued August, 1986 to Johnson is an example of a brake lining wear sensor and indicator circuit. In the Johnson patent, the brake lining wear sensor includes a metal contact secured to a grounded brake lining support plate. When the brake lining is not worn, a semiconductive ceramic bushing establishes an electrical resistance between the contact and the support plate. When the brake lining is worn, the contact touches a grounded brake rotor or drum thereby causing a short to ground. Furthermore, the sensor is coupled to a lead wire to an indicator circuit that tests for resistance values to determine whether the contact is electrically grounded to the rotor.
The aforementioned patents may disclose suitable strategies for determining the brake lining wear status and relaying this information via an indicator apparatus. The prior art, however, generally requires that the sensor is either mounted external to the caliper assembly, associated with or part of the friction pad(s), and/or has a portion worn away along with the friction pad. This may increase maintenance and manufacturing costs by increasing parts and installation time. Therefore, it would be desirable to achieve a disc brake lining wear monitoring system and method that overcomes the aforementioned and other disadvantages.
One aspect of the invention provides a system for monitoring brake pad wear. The system comprises a vehicle disc brake caliper assembly including a boot assembly and at least one friction pad. The system further comprises at least one caliper bolt including a caliper bolt switch point, the caliper bolt movably positioned within the boot assembly. A conductive element is positioned a predetermined distance from the caliper bolt switch point. An electrical circuit is switched when the conductive element contacts the switch point. The contact is established when the friction pad wears to a predetermined level corresponding to the predetermined distance.
The conductive element may comprise a wire terminating in a flexible wiper member positioned adjacent to the caliper bolt. An insert member may retain the conductive element in a fixed position relative to the boot assembly during movement of the caliper mounting bolt. A brake wear indicator assembly comprising an indicator unit may be electrically attached to the conductive element. The brake wear indicator assembly may be capable of indicating brake wear status to a vehicle operator based upon the switching of the electrical circuit. The predetermined distance may be determined based upon a desirable wear allowance of the brake pad.
The conductive element may be movably positioned in an undercut region. The switch point may be positioned at one end of the undercut region. A closed circuit may be formed when the conductive element contacts the switch point.
The conductive element may be movably positioned in electrical contact with the caliper bolt. The conductive element may remain in electrical contact with the caliper bolt until the conductive element contacts the switch point. The switch point may comprise an undercut region. An open electrical circuit may be formed when the conductive element contacts the switch point.
Another aspect of the invention provides for a method of monitoring brake pad wear. The method provides a caliper bolt including a caliper bolt switch point. A conductive element is positioned a predetermined distance from the caliper bolt switch point. The predetermined distance is progressively decreased as the brake pad wears. An electrical circuit is switched when the conductive element contacts the caliper bolt switch point.
The conductive element may comprise a wire terminating in a flexible wiper member positioned adjacent to the caliper bolt. An insert member may retain the conductive element in a fixed position relative to a boot assembly during movement of the caliper mounting bolt. Brake wear status may be indicated to a vehicle operator based upon the switching of the electrical circuit. The predetermined distance may be determined based upon a desirable wear allowance of the brake pad.
The conductive element may be movably positioned in an undercut region. The switch point may be positioned at one end of the undercut region. A closed circuit may be formed when the conductive element contacts the switch point.
The conductive element may be movably positioned in electrical contact with the caliper bolt. The conductive element may remain in electrical contact with the caliper bolt until the conductive element contacts the switch point. The switch point may comprise an undercut region. An open electrical circuit may be formed when the conductive element contacts the switch point.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.